Make your mind your not going to cum, just set a goal of enjoying a good, fun experience. Take your mind off the 'money shot' & just fool around. After all enjoying the action prior to an orgasm is the entire point & pleasure of love making , if your cork doesn't pop.... so what. If you've had fun & it you both feel close is not cumming that important?
Some of the most passionate sessions we've had I've not climaxed into Mrs Duck- Its not the end of the world. Don't worry about it and just be a mucky little tart, drink Champagne, eat messy food. A nice sexy candlelit massage is nice on so many levels, blindfolds, sexy lingerie all add to mood. It should be fun if nothing else!
Just have FUN,
Enjoy